The present invention relates to an image processing method and apparatus for performing processing on inputted image data and generating data to be used by an output apparatus, and an image forming apparatus for processing inputted image data and forming an image based on the processed image data.
As the resolution capability of a display apparatus or a recording apparatus has improved in recent years, a large number of apparatuses having resolution capability superior to resolution of image data used in a host computer have been developed.
For a circuit which reads and writes such high-resolution image data at high speed, for instance, a graphic processor disclosed in Japanese Patent Publication No. 7-109550 or No. 7-109549 has been suggested. These publications disclose, for instance, a structure for reading multivalued data, representing one pixel by 4 bits of data, out of a memory and outputting the data in accordance with a display position where the pixel is displayed, and also a structure for performing logical operations on the image data to be outputted based on mask data and color data stored in a mask register.
However, the foregoing conventional technique does not take into account converting resolution of image data, from 300.times.300 dpi used by e.g. a host computer or the like, to 600.times.1200 dpi used by an image output apparatus having a higher resolution capability. Moreover, performing resolution conversion on inputted image data and generating binary data (i.e. binary data having a resolution of 600.times.1200 dpi) where one bit of the converted image data corresponds to one nozzle of a printhead, are conventionally executed by software. When such processing is performed by software, a large load is added to the host computer executing the software. Furthermore, in a case where such high-resolution data is transferred from a host computer to an image output apparatus, the time required to transfer the data between the host computer and image output apparatus is about twice as long as a case of transferring multivalued data having resolution of 300.times.300 dpi where 4 bits represent 1 pixel.
Note that in order to reduce the data transfer time between the host computer and image output apparatus, it has been suggested to transfer the image data having a resolution of 300 dpi without being processed from the host computer to the image output apparatus, and have the image output apparatus perform resolution conversion suitable to the apparatus for outputting an image. However, in this case, the image output apparatus temporarily stores the received data in a RAM and performs resolution conversion, or performs resolution conversion by dedicated hardware. Although the data transfer time is reduced by this method, the time required for resolution conversion is increased; and as a result, throughput declines. Moreover, even if dedicated hardware is provided in the image output apparatus, it is problematic in that the memory capacity of the RAM must be increased.